Digital Signal Processing Techniques and Applications in Radar Image Processing

5

RADAR MODULATION AND TARGET DETECTION TECHNIQUES

In Chapter 4, we mentioned that various waveforms can be used by radars to detect the range and/or speed of a target. In this chapter, we discuss several types of these waveforms. Section 5.1 reviews amplitude modulation (AM)-based radars, including continuous–wave radar and pulse–Doppler radar. Section 5.2 describes target detection techniques on AM-based radar. Frequency modulation (FM)-based radars are covered in Section 5.3, including linear frequency modulation (LFM), pulsed LFM, continuous-wave LFM (CWLFM), and stepped frequency modulation (SFM). The target detection techniques for FM-based radar, which utilize the in-phase–quadrature-phase demodulator and matched filtering, are discussed in Section 5.4.

5.1 AMPLITUDE MODULATION (AM) RADAR

Amplitude modulation (AM) is a modulation technique in which the amplitude of the carrier is varied in accordance with some characteristics of the baseband modulating signal. It is the most common form of modulation because of the ease with which the baseband signal can be recovered from the transmitted signal.

An AM signal p(t) can be described in terms of carrier frequency f_c and baseband signal p_b(t) by the following equation:

Letting the modulating signal p_b(t) be a sinusoidal signal as p_b(t) = A_m cos (2πf_at), Eq. (5.1) then becomes

In general A_m < 1; otherwise a phase reversal occurs ...